Background: Previous studies have shown that alexithymia is associated with gene polymorphisms that regulate the availability of serotonin (5-HT) in the brain. Since the 5-HT network is involved in interferon (IFN)-induced depression, this paper aimed to investigate the role of alexithymia and the functional gene variants of the 5-HT1A receptor (HTR1A) and the 5-HT transporter (5-HTTLPR) in induction of depression during antiviral treatment. Methods: The depressive symptoms of 130 consecutive patients with chronic hepatitis C and no current psychopathology were measured during treatment with IFN and ribavirin (6-12 months) and at a 6-month follow-up. At baseline, alexithymia and 2 genotypes (5-HTTLPR and HTR1A) were also assessed. Results: Patients with homozygosity for HTR1A-G and 5-HTTLPR long alleles had significantly higher levels of alexithymia. After controlling for sociodemographic and disease-related factors, alexithymia and HTR1A-G polymorphism, both separately (20-22%) and jointly (14-16%), significantly and independently predicted the development of IFN-induced depression. Conclusions: Subjects carrying HTR1A-G and 5-HTTLRP double long alleles are more vulnerable to alexithymia. Also patients with a higher level of alexithymia and the HTR1A-G gene variant are more vulnerable to experiencing IFN-induced depressive symptoms. The clinical implications of targeting alexithymia and HTR1A receptors as a possible treatment option for mood disorders should be investigated in further studies.